Difficulty is frequently encountered in the introduction of longitudinal and bending forces into connecting fittings of highly stressed parts of fiber-reinforced plastic (FRP) because the resistance of FRP to alternating shearing stresses is only about one-twentieth of the resistance to alternating tensile stresses. It is therefore necessary to design the connecting regions of these parts so that the shearing stresses appearing in the FRP are reduced to a minimum.
Presently known arrangements are generally sufficient for the introduction of tensile forces. These arrangements provide embracing of an end loop of FRP by a shell of FRP or metal. For the introduction of compressive forces, this measure is not sufficient. The introduction of compressive forces over a wedge arranged inside an end loop of FRP, which is connected to a bush receiving a connecting bolt, is known. For very large reaction forces appearing in the connecting fittings, however, the transmission of shear between the wedge and the end loop is relatively too weak.
In order to improve the transmission of compressive forces, it is known to embrace the end loops additionally on all sides, for example, with metal fittings consisting of two parts. These fitting parts transmit the reaction forces produced by the bending forces to the front part of the FRP formed loop by way of compressive forces. This has the disadvantage, however, that harmful relative movements appear between the loop and the fittings, particularly under alternating stresses.
Another disadvantage in the use of metal fittings is that, due to the different coefficient of thermal expansion between the two materials, metal/plastic, either thermal stresses or a gap will appear at extremely high or low temperatures. This renders the transmission of the compressive forces difficult, so that the entire connecting fittings will be destroyed in the course of time, for example, under alternating bending stresses.